Add missing #include, fixes the warning:

libvo/vo_png.c:147: warning: implicit declaration of function 'imgfmt2pixfmt'


git-svn-id: svn://svn.mplayerhq.hu/mplayer/trunk@30469 b3059339-0415-0410-9bf9-f77b7e298cf2

Author: diego

libvo/vo_png.c

@@ -31,6 +31,7 @@
 #include <unistd.h>
 
 #include "config.h"
+#include "fmt-conversion.h"
 #include "mp_msg.h"
 #include "mp_msg.h"
 #include "help_mp.h"